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Author Topic: Space and Time  (Read 5500 times)

Offline Ben

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Space and Time
« on: 03/10/2006 13:37:56 »
If time is said to slow down for an object which is moving fast relative to another object, does this mean that for a planet in a solar system on the outskirts of a spinning galaxy (which is moving fast) that time appears slower than for a planet in a solar system near the centre of a galaxy (which is moving more slowly)?

Will this effect make a difference to the time experienced on each of the planets over hundreds of millions of years?


 

Offline ukmicky

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Re: Space and Time
« Reply #1 on: 03/10/2006 23:56:54 »
I would say yes over a very very long period of time  and then throw in a big but, because with the exception of stars orbiting very close to a SMBH galaxies and their stars cant and don't rotate anywhere near the relativistic speeds required to make the effects of time dilation noticeable.



Michael
« Last Edit: 04/10/2006 00:33:30 by ukmicky »
 

Offline bostjan

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Re: Space and Time
« Reply #2 on: 04/10/2006 05:17:35 »
Also, the gravitational potential is slightly higher in the center of the universe, so the effects of general relativity, might cancel out any miniscule effects of special relativity.
 

Offline Soul Surfer

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Re: Space and Time
« Reply #3 on: 04/10/2006 11:12:00 »
Ben you've got it wrong about the way galaxies rotate.  They don't rotate like wheels which are rigid structures and the edges go quicker than the middles. They rotate like the solar system in which the bits closest to the middle go faster than the bits at the edge. However the bits at the edge dont go quite as slow as one wiuld expect if you counted up the stars and added their mass into the gravitiational attraction needed to keep them in orbit.  that's what makes us think that there is dark matter around there somewhere.  As for time dilation  very few large objects go fast enough to experience much you have to go very close to the velocity of light to have much effect.

I really do'nt understand why peope are so interested in relatavistic time shifts Relatavistic time dilation is totally irrelevant for most objects because most things just don't have precise times associated with them.  Even people time shifted by a year are very similar and as for a few seconds no one would notice.  Remember you get over a biological clock shift of a few hours on a plane in a few days.  About the only non living object that is time sensitive is a decaying radioactive isotope  and even that is only sensitive to the half life.

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Offline syhprum

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Re: Space and Time
« Reply #4 on: 04/10/2006 14:24:52 »
I think people are fascinated with the idea of time travel, just think you go back to shoot a dinosaur tread on a butterfly and when you come back to the present you find everything changed

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« Last Edit: 04/10/2006 14:25:24 by syhprum »
 

Offline bostjan

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Re: Space and Time
« Reply #5 on: 05/10/2006 05:23:27 »
yeah but you need a flux capacitor and an old 1960's toaster to do that.  ;)
 

Offline Nieuwenhove

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Re: Space and Time
« Reply #6 on: 05/10/2006 17:47:48 »
quote:
Originally posted by Ben

If time is said to slow down for an object which is moving fast relative to another object, does this mean that for a planet in a solar system on the outskirts of a spinning galaxy (which is moving fast) that time appears slower than for a planet in a solar system near the centre of a galaxy (which is moving more slowly)?

Will this effect make a difference to the time experienced on each of the planets over hundreds of millions of years?



Nobody seems to have mentioned that these time dilations are relative ! Suppose star A moves faster than star B, then both have a velocity relative to each other. A person on a planet near star A will see another person near star B ageing slower (maybe a microsecond over a lifetime) while a person near star B will see the other person (near star A) ageing slower. Now, I have used an argument from special relativity which is not really applicable since we are dealing with accelerated motion. There is some similarity here with the twin paradox, though it is more complicated here. So, one should use general relativity here which will become quit complicated. Any suggestions ?
 

Offline syhprum

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Re: Space and Time
« Reply #7 on: 05/10/2006 21:15:29 »
I can easily get hold of a 1960's toaster but I have no idea what a 'flux capacitor' is.
please enlighten me so I can get dino hunting.

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Offline lightarrow

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Re: Space and Time
« Reply #8 on: 10/10/2006 13:16:00 »
quote:
Originally posted by Nieuwenhove

quote:
Originally posted by Ben

If time is said to slow down for an object which is moving fast relative to another object, does this mean that for a planet in a solar system on the outskirts of a spinning galaxy (which is moving fast) that time appears slower than for a planet in a solar system near the centre of a galaxy (which is moving more slowly)?

Will this effect make a difference to the time experienced on each of the planets over hundreds of millions of years?

Nobody seems to have mentioned that these time dilations are relative ! Suppose star A moves faster than star B, then both have a velocity relative to each other. A person on a planet near star A will see another person near star B ageing slower (maybe a microsecond over a lifetime) while a person near star B will see the other person (near star A) ageing slower. Now, I have used an argument from special relativity which is not really applicable since we are dealing with accelerated motion. There is some similarity here with the twin paradox, though it is more complicated here. So, one should use general relativity here which will become quit complicated. Any suggestions ?
Yes, this was already covered even in this forum (see THE TWINE paradox: http://www.thenakedscientists.com/forum/topic.asp?TOPIC_ID=5174).

It's called EHRENFEST PARADOX: http://en.wikipedia.org/wiki/Ehrenfest_paradox

See also:http://en.wikipedia.org/wiki/Born_coordinates
quote:
Summary
Observers riding on a rigidly rotating disk will conclude from measurements of small distances between themselves that the geometry of the disk is non-euclidean. Regardless of which method they use, they will conclude that the geometry is well approximated by a certain Riemannian metric, namely the Langevin-Landau-Lifschitz metric. This is in turn very well approximated by the geometry of the hyperbolic plane (with the constant negative curvature -3w^2). But if these observers measure larger distances, they will obtain different results, depending upon which method of measurement they use! In all such cases, however, they will most likely obtain results which are inconsistent with any Riemannian metric. In particular, if they use the simplest notion of distance, radar distance, owing to various effects such as the asymmetry already noted, they will conclude that the "geometry" of the disk is not only non-euclidean, it is non-Riemannian


I have to say that, unfortunately, I was not able to fully understand everything said in those files.

This is what I have understood, someone correct me if I'm wrong:

1.Even on a circular ring which rotates with constant speed, it's not possible to assign a unique time to all the travellers along the ring.

2.The geometry of the ring is not euclidean (flat) anylonger, so circumference = 2*(pi)*R it's not true anylonger (so, not even v = omega*R is true anylonger) ; specifically, the radius R should be greater than the circumference.

3.Not even something simple has the radius R has a unique meaning: from an observer in the center of the ring it has the value R, for an abserver travelling along the ring, it has another value!
« Last Edit: 12/10/2006 08:21:36 by lightarrow »
 

Offline Soul Surfer

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Re: Space and Time
« Reply #9 on: 10/10/2006 23:36:32 »
Again you are running into problems because you are thinking of rigid body dynamics instead of independent particle dynamics when you are invoved in things goig at relatavistic speeds.

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Offline lightarrow

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Re: Space and Time
« Reply #10 on: 11/10/2006 11:26:07 »
And how can we solve the problem considering only independent particles travelling along a circumference?
 

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Re: Space and Time
« Reply #10 on: 11/10/2006 11:26:07 »

 

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